The Enhanced Uplink Channel (E-DCH) is a dedicated channel used by User Equipments (UEs) to transmit data in the uplink. Up to Release 8, a UE could only transmit data on one E-DCH. Third Generation Project Partnership (3GPP) is currently standardizing Dual-Cell HSUPA (High Speed Uplink Packet Access) also known as Dual Carrier HSUPA for HSPA in Release 9. In this release, a UE can transmit one E-DCH on each one of up to two uplink carriers. There have also been proposals in 3GPP to introduce multi-carrier High Speed Packet Access (HSPA) with 3-4 carriers.
When a UE configured for Dual Carrier High Speed Uplink Packet Access (DC-HSUPA) enters the CELL_DCH state only the primary uplink (hereinafter this refers to the serving E-DCH cell that corresponds to the serving HS-DSCH cell) will be activated. The other uplink carriers (hereon after referred to as secondary uplink carriers) will thus initially be deactivated. In order to allow the UE to transmit on these secondary uplink carriers the radio base station, also referred to as Node B needs to send a High Speed Shared Control Channel (HS-SCCH) activation order. Upon receiving such an order, the UE starts sending on the Dedicated Physical Control Channel (DPCCH) so that uplink synchronization can be established. Once this has been achieved the UE may start transmitting on the secondary carrier(s). Since UEs generally can achieve higher data rates by transmitting on multiple carriers simultaneously (as opposed to only transmit data on a the primary uplink carrier) the situation in which the Node B sends an activation order for the secondary uplink(s) just after entering CELL_DCH is believed to be frequently occurring.
Currently in 3GPP it has been agreed, see 3GPP Tdoc R1-092243, “Notes from RAN1 adhoc session on DC-HSUPA, DC-HSDPA MIMO, 2 ms TTI Extension and TxAA extension for non-MIMO UEs” [2] 3GPP Tdoc R1-092254, “Draft 25.214 CR for Introduction of DC-HSUPA” that when a UE receives an HS-SCCH order for activating the secondary uplink carrier the initial DPCCH transmit power should be computed as:Uplink DPCCH transmit power=PDCCH,1−UE_Sec—Tx_Power_Backoff.  (equation 1)
Here PDCCH,1 is the DPCCH transmit power on the primary uplink carrier and UE_Sec_Tx_Power_Backoff is a parameter that is configured by the Radio Network Controller (RNC) when the UE enters CELL_DCH. In principle, this could take on either positive or negative values. The latter implies that the initial DPCCH power on the secondary carrier exceeds the DPCCH power used on the primary carrier. Note also that the back-off could reflect both static parameters (such as potential differences in carrier frequency) and dynamic parameters (e.g., cell load) which change over time.
For example, if the load on the secondary uplink carrier at the time-instance the UE enters CELL_DCH is higher than the loading on the primary carrier and the Node B would activate the secondary carrier within a time-period so short so that the loading conditions on the carriers would not have changed it could be advantageous to use a negative back-off value (i.e. an initial DPCCH power on the secondary that exceeds the DPCCH power level on the primary carrier) since this would reduce the time-duration until synchronization for the secondary uplink carrier is achieved.
There is a constant desire to improve performance in existing cellular radio systems. Hence, there exist a need for a method and a system that enables an improved setting of the back off for secondary carriers in a Multi carrier cellular radio system.